As a technique regarding a lock device used in a seat reclining apparatus, for example, Patent Document 1 has disclosed a technique below. This lock device is configured substantially as in embodiments of the present invention described later. More specifically, as shown in FIGS. 7 and 8, a lower guide 51, an upper gear 52, a ring holder 53, three poles 54, a cam 55, and a spring 56 are provided. Internal teeth 52a are formed on an inner circumferential face of the upper gear 52. On the other hand, external teeth 54a that become engaged with the internal teeth 52a are formed on the outer peripheral end faces of the three poles 54. The cam 55 swings between a lock phase and a release phase, thereby causing the three poles 54 to become synchronously engaged with or released from the internal teeth 52a. The spring 56 biases the cam 55 in a direction to cause the poles 54 to become engaged with the internal teeth 52a. The lower guide 51 has guide portions 57 for guiding the cam 55 and the poles 54. The lower guide 51 and the upper gear 52 are opposed to each other and combined in a relatively rotatable manner.
As shown in FIG. 8, radial movement of the cam 55 is regulated by a guide face 57a that is constituted by the inner peripheral face of the guide portion 57 formed on the lower guide 51, and the cam 55 is guided so as to be swingable only in the peripheral direction. It should be noted that there is a clearance between the guide face 57a and a guided face 55a on the outer periphery of the cam 55, and the cam 55 can loosely move to some extent in the radial direction. Herein, the clearance between the guide face 57a and the guided face 55a of the cam 55 is wide in a state where the cam 55 is close to the lock phase, and narrow in a state where the cam 55 is close to the release phase. On the other hand, in a state where the cam 55 is in the lock phase, the three poles 54 that have been pushed by the cam 55 outward in the radial direction become engaged with the internal teeth 52a of the upper gear 52. Accordingly, the cam 55 is supported by the three poles 54 with respect to the upper gear 52.
Patent Document 1: JP 2002-101996A